Method and device for compensating the transmission behavior of a measuring, regulating or control device

ABSTRACT

The present invention relates to a method for compensating the transmission behavior of a measuring, regulating or control device wherein the output values of the device are modified by correction factor which is approximately determined for the associate input values in accordance with the transmission behavior of the device. A compensating circuit operates to provide first order differentiation of an output signal delivered from the device a plurality of times until a desired correction of the output signal has been absolved.

FIELD OF THE INVENTION

The present invention relates to a method for compensating thetransmission behavior of a measuring, regulating or control device, inparticular of a dynamic length measuring system in accordance with thehigh pressure measurement method, in which the output values of thearrangement are modified by a correction function which is approximatelydetermined for the associated input values in accordance with thetransmission behavior of the arrangement.

BACKGROUND OF THE INVENTION

It is known that measuring, regulating and control arrangements have atransmission behavior. The output value in particular lags behind theinput value due to the inertia of the said arrangements. This means thatthe output value only reaches the value of the input value after acertain start-up time. This leads to fast, dynamic measurements notbeing able to be carried out.

It is therefore known to compensate the transmission behavior of sucharrangements in that a function inverse to the transmission function isapplied to the output value. The transmission function is usuallyapproximately described as a differential equation for this, whose orderdepends on the respective arrangement. It is a problem that differentialequations of a higher order cannot be realized, or can only be realizedat great cost and complexity, from a technical circuit aspect. Thecompensation of the transmission behavior of such an arrangement iscorrespondingly complicated.

SUMMARY OF THE INVENTION

It is the underlying object of the invention to provide an improvedmethod of the kind initially named and an apparatus for the carrying outof the method. The compensation should in particular be able to berealized more easily.

This object is satisfied in that a linear differential equation of thefirst order is used as the approximated correction function and in thatthe output values are modified by this correction function several timesin succession by the modified output value again being modified, and soforth.

The idea of the invention therefore consists of always only usingdifferential equations of the first order for compensating thetransmission behavior, irrespective of the kind of arrangement and ofits transmission behavior, and to carry out this compensation so oftenin the manner of an iteration process that a desired degree ofcompensation or a desired acceleration of the measurement, that is timeuntil the reaching of the end value, is achieved. For example, adifferential equation of the fourth order of a conventional method isreplaced by using a differential equation of the first order four timeson the starting values to obtain the same degree of compensation. Theinverse transmission function can thus be easily realized from atechnical circuit aspect. Since, moreover, a repeated use of thiscircuit is unproblematic, the compensation overall is not complicated.

In accordance with an embodiment of the invention, the correctionfunction has the following form:${{S^{\prime}(t)} = {{S(t)} + {k \times \frac{{S(t)}}{t}}}},$

where S(t) is the value to be modified, S′(t) is the modified value andk is a constant. In this connection, a separate constant k is preferablyfixed for each correction step. A very good and fast adaptation of theoutput value to the input value can be achieved with this function andthe fixing of independent constants k for each correction step.

It is preferred for the constant k to be determined such that as fewcorrection steps as possible are required for the desired correction.The compensation circuit is thereby simplified and the processaccelerated.

In accordance with a further embodiment in accordance with theinvention, suitable constants k are determined for the correction stepsby trials. It has been found that very good results can be achieved inthis manner.

In accordance with a further embodiment in accordance with theinvention, the constants k for the correction steps are determinedautomatically. This means that the constants k are varied for so long bya routine to be determined until they deliver an optimum result.

In accordance with a further embodiment of the invention, the modifiedvalues are directed through an attenuation member, in particular a lowpass filter, in the final correction step. An overshooting of thecorrected value over the actual value is hereby avoided.

In accordance with a further embodiment of the invention, the end valueof the correction is averaged over a time interval. Noise occurring dueto the attenuation or for another reason can be compensated in this way.

It is preferred if the averaging of the end value is begun after afixable start-up time. It can thus be ensured that the end value hasalready stabilized sufficiently.

In accordance with a further embodiment of the invention, the averagingis begun in response to a signal which can be delivered to the systemfrom outside. In this way, the possibility is provided of startingaveraging individually and in particular in dependence on externalparameters.

An apparatus for carrying out of method in accordance with claim 1 hasthe features set forth in claim 11, moreover, optionally, means forattenuating the modified value, in particular a low pass filter, andmeans for averaging the end value of the modification as well as meansfor outputting the corrected value. The apparatus is preferably designedsuch that the number of correction steps can be adjusted. The precisionand the acceleration of the correction process can thus be selected.

In accordance with a further embodiment of the invention, the point intime of the averaging can be adjusted. In accordance with yet anotherembodiment of the invention, the degree of attenuation, in particularthe limiting value of the low pass filter, can be adjusted.

The method in accordance with the invention and the apparatus inaccordance with the invention are preferably used in length measurementsin accordance with the high pressure measurement method which work witha measuring nozzle and a front nozzle and with a pressure sensor infront of the front nozzle and a pressure sensor between the front nozzleand the measuring nozzle, that is without the otherwise usual bridgecircuit. In such a method and apparatus, known for example from DE 19733 984 A1, the problem often occurs that the pressure sensors arerelatively far away from the measuring nozzle, since there is notsufficient room present for this in the proximity of the measuringnozzle. The response time of the measuring arrangement is thereforecorrespondingly long.

The response time can be compensated in a simple and skilled manner bythe method in accordance with the invention and by the apparatus inaccordance with the invention so that such measurements can beaccelerated with a comparatively small effort. Fast dynamic lengthmeasurements thus become possible.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention is represented in the drawing and will bedescribed in the following. There are shown, in each case in a schematicrepresentation:

FIG. 1 the basic principle of a pneumatic length measurement without abridge circuit;

FIG. 2 the use of such a measuring arrangement with a compensationapparatus in accordance with the invention;

FIGS. 3a and 3 b provide a comparison of the compensated andnoncompensated measured values of such an arrangement, respectively; and

FIG. 4 is a block diagrammatic illustration of signal flow from thetransducer through the compensating apparatus.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows the basic set-up of a measuring arrangement for thecarrying out of a pneumatic length measurement such as is described inDE 197 33 984 A1. The measuring arrangement shown includes a frontnozzle 1, a measuring nozzle 2, a first pressure sensor 3 arranged infront of the front-nozzle 1 and a second pressure sensor 4 arrangedbetween the front nozzle 1 and the measuring nozzle 2. A deflectionplate 5 representative of a work piece to be measured is shown in frontof the air outlet opening of the measuring nozzle 2.

Compressed air is delivered to the system in accordance with arrow 6from a pressure source (not shown). When the distance X between thedeflection plate 5 and the measuring nozzle 2 changes, the pressurevalue p₂ measured by the pressure sensor 4 changes. The distance X isdetermined from this while taking into account the pressure value p₁measured by the first pressure sensor 3.

FIG. 2 shows the application of the principle described with referenceto FIG. 1 for the measurement of the interior diameter D of a hollowarticle 7. A measuring head 8 includes two air outlet openings 9 whichare disposed on opposite side and which are connected to a pressure line11 connected to the measuring head 8 via a pressure passage 10. Thepressure line 11 is connected at the other end to a transducer 12 inwhich the front nozzle and the two pressure sensors 13 and 14 areaccommodated and which is connected to a pressure source. The signaloutput of the transducer 12 is connected to a compensation apparatus 15in accordance with the invention whose output in turn makes availablethe end signal. An increase in the diameter D results in a fall in themeasured pressure p₂ and vice versa.

As best illustrated in FIG. 4, the compensation apparatus in particularincludes a circuit with which the compensation function, which, inaccordance with the invention, is a differential equation of the firstorder, is realized and means to apply the compensation function aplurality of times to an output signal delivered by the transducer 12.This means the differential equation fixed in the circuit is applied tothe signal delivered by the transducer 12 and this differential equationis again applied to the signal resulting therefrom, and so on, until adesired acceleration is achieved or a previously fixed number of suchcorrection steps has been absolved.

The correction function fixed in the circuit can have the followingform, for example:

${{S^{\prime}(t)} = {{S(t)} + {k \times \frac{{S(t)}}{t}}}},$

where S(t) is the value to be modified, S′(t) is the modified value andk is a constant. A separate constant k is preferably fixed for eachcorrection step in this connection, with these constants k being able tobe determined either by trials or automatically for the respectivearrangement. In this connection, the constants k are determined suchthat only a few correction steps are needed. In a high pressuremeasuring process of the previously described kind, good accelerationvalues were able to be achieved with four correction steps and suitableconstants k.

FIGS. 3a and 3 b show measurements of the interior diameter D of thearticle 7 carried out with the apparatus of FIG. 2. For this purpose,the measuring head 8 was moved into the article 7 and back out againfive times at different speeds. The hose length during the carrying outof the measurement was 1.5 m. The transducer was statically adjusted tozero for the nominal diameter D before the measurement.

FIG. 3a shows the measuring result when using the compensation apparatusin accordance with the invention and FIG. 3b without compensation. Itcan clearly be recognized that the measured value is reached much fasterwith the compensation in accordance with the invention than without. Itcan also be recognized that with very short measurements, the measuredvalue is still reached with the compensation in accordance with theinvention, while this is no longer the case without compensation.

As represented and stated, a substantial acceleration of the measurementis achieved by the method in accordance with the invention and by theapparatus in accordance with the invention. Fast, dynamic measurementscan thus be carried out. The compensation is uncomplicated due to thecompensation method in accordance with the invention and can be realizedwith comparatively simple circuits.

REFERENCE NUMERAL LIST

 1 front nozzle  2 measuring nozzle  3 first pressure sensor  4 secondpressure sensor  5 deflection plate  6 arrow  7 article  8 measuringhead  9 air outlet opening 10 air passage 11 air line 12 transducer 13first pressure sensor 14 second pressure sensor 15 compensationapparatus X distance D diameter

What is claimed is:
 1. A method for compensating the transmissionbehavior of a measuring, regulating or control arrangement, inparticular of a dynamic length measuring arrangement in accordance witha high pressure measurement method, said compensating method comprisingthe steps of: determining a correction function for associated inputvalues of the arrangement in accordance with the transmission behaviorof the arrangement wherein said correction function is a lineardifferential equation of the first order; and reiteratively modifyingoutput values from the arrangement by the correction function aplurality of times in succession to obtain an end value.
 2. A method inaccordance with claim 1, characterized in that the repeatedly appliedcorrection function has the following form:${{S^{\prime}(t)} = {{S(t)} + {k \times \frac{{S(t)}}{t}}}},$

where S(t) is the value to be modified, S′(t) is the modified value andk is a constant.
 3. A method in accordance with claim 2, characterizedin that a separate constant k is fixed for each correction step.
 4. Amethod in accordance with claim 3, characterized in that the constants kare determined such that as few corrections steps as possible are neededfor the desired correction.
 5. A method in accordance with claim 3,characterized in that suitable constants k for the correction steps aredetermined by trials.
 6. A method in accordance with claim 3,characterized in that suitable constants k for the correction steps aredetermined automatically.
 7. A method in accordance with claim 1,characterized in that the modified values are directed through anattenuation member, in particular a low pass filter, in the lastcorrection step.
 8. A method in accordance with claim 7, characterizedin that the end value of the correction is averaged over a timeinterval.
 9. A method in accordance with claim 8, characterized in thatthe averaging of the end value is started after a fixable start-up time.10. A method in accordance with claim 9, characterized in that theaveraging is started in response to a start signal deliverable to thesystem from the outside.
 11. An apparatus for compensating thetransmission behavior of a measuring, regulating or control arrangement,in particular of a dynamic length measuring arrangement in accordancewith a high pressure measurement method, said apparatus comprising:means for modifying output values of the arrangement by a correctionfunction wherein said correction function is determined for theassociated input values in accordance with the transmission behavior ofthe arrangement, and wherein said means for modifying the output valuesare designed such that a linear differential equation of the first orderis used as the correction function, and wherein the output values arereiteratively modified by said correction function a plurality of timesin succession to obtain an end value.
 12. An apparatus in accordancewith claim 11, characterized in that an attenuation member, inparticular a low pass filter is provided, through which the modifiedvalues can be directed.
 13. An apparatus in accordance with claim 11,characterized in that means are provided for averaging the modifiedvalue.
 14. An apparatus in accordance with claim 11, characterized inthat means for outputting the end value are provided.
 15. An apparatusin accordance with claim 11, characterized in that the number of thecorrection steps is adjustable.
 16. An apparatus in accordance withclaim 13, characterized in that the starting point in time of theaveraging is adjustable.
 17. An apparatus in accordance with claim 12,characterized in that the magnitude of the attenuation, in particularthe limit value of the low pass filter, is pre-settable.
 18. Use of themethod in accordance with claim 1 for the length measurement inaccordance with the high pressure measurement method, in particularwhile using an apparatus having a front nozzle (1) and a measuringnozzle (2), having a first pressure sensor (3) in front of the frontnozzle (1) and having a second pressure sensor (4) between the frontnozzle (1) and the measuring nozzle (2).
 19. Use of a method inaccordance with claim 11 for the length measurement in accordance withthe high pressure measurement method, in particular while using anapparatus having a front nozzle (1) a measuring nozzle (2), a firstpressure sensor (3) in front of the front nozzle (1) and a secondpressure sensor (4) between the front nozzle (1) and the measuringnozzle (2).